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WO2013024596A1 - Procédé de codage d'informations de mémoire holographique, procédé d'enregistrement de mémoire holographique et dispositif de mémoire holographique - Google Patents

Procédé de codage d'informations de mémoire holographique, procédé d'enregistrement de mémoire holographique et dispositif de mémoire holographique Download PDF

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Publication number
WO2013024596A1
WO2013024596A1 PCT/JP2012/005161 JP2012005161W WO2013024596A1 WO 2013024596 A1 WO2013024596 A1 WO 2013024596A1 JP 2012005161 W JP2012005161 W JP 2012005161W WO 2013024596 A1 WO2013024596 A1 WO 2013024596A1
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Prior art keywords
data
phase
information
holographic memory
signal
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PCT/JP2012/005161
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English (en)
Japanese (ja)
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修 的場
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国立大学法人神戸大学
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Priority to US14/130,445 priority Critical patent/US8976638B2/en
Priority to JP2013528920A priority patent/JP5896362B2/ja
Publication of WO2013024596A1 publication Critical patent/WO2013024596A1/fr

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    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/007—Arrangement of the information on the record carrier, e.g. form of tracks, actual track shape, e.g. wobbled, or cross-section, e.g. v-shaped; Sequential information structures, e.g. sectoring or header formats within a track
    • G11B7/00772—Arrangement of the information on the record carrier, e.g. form of tracks, actual track shape, e.g. wobbled, or cross-section, e.g. v-shaped; Sequential information structures, e.g. sectoring or header formats within a track on record carriers storing information in the form of optical interference patterns, e.g. holograms
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H1/00—Holographic processes or apparatus using light, infrared or ultraviolet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
    • G03H1/26—Processes or apparatus specially adapted to produce multiple sub- holograms or to obtain images from them, e.g. multicolour technique
    • G03H1/2645—Multiplexing processes, e.g. aperture, shift, or wavefront multiplexing
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B20/00—Signal processing not specific to the method of recording or reproducing; Circuits therefor
    • G11B20/10—Digital recording or reproducing
    • G11B20/18—Error detection or correction; Testing, e.g. of drop-outs
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H2240/00—Hologram nature or properties
    • G03H2240/10—Physical parameter modulated by the hologram
    • G03H2240/13—Amplitude and phase complex modulation
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B2220/00—Record carriers by type
    • G11B2220/20—Disc-shaped record carriers
    • G11B2220/25—Disc-shaped record carriers characterised in that the disc is based on a specific recording technology
    • G11B2220/2504—Holographic discs; Holographic digital data storage [HDDS]
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/004—Recording, reproducing or erasing methods; Read, write or erase circuits therefor
    • G11B7/0065—Recording, reproducing or erasing by using optical interference patterns, e.g. holograms
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/08—Disposition or mounting of heads or light sources relatively to record carriers
    • G11B7/085—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam into, or out of, its operative position or across tracks, otherwise than during the transducing operation, e.g. for adjustment or preliminary positioning or track change or selection
    • G11B7/08547—Arrangements for positioning the light beam only without moving the head, e.g. using static electro-optical elements
    • G11B7/08564—Arrangements for positioning the light beam only without moving the head, e.g. using static electro-optical elements using galvanomirrors
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
    • G11B7/1392—Means for controlling the beam wavefront, e.g. for correction of aberration

Definitions

  • the present invention relates to information encoding technology for holographic memory.
  • the holographic memory records an interference pattern formed by signal light (or object light) and reference light as a spatial distribution of refractive index.
  • the recording device of the holographic memory encodes data two-dimensionally, assigns the encoded data to the signal light by an optical modulator, and records the data on a recording medium in units of pages.
  • the light modulator a large number of pixels are arranged in rows and columns, and each pixel can independently transmit and block light, and an arbitrary ON / OFF bit pattern is two-dimensionally expressed.
  • the intensity of the light is spatially modulated according to the two-dimensional pattern of the optical modulator.
  • the recording density of the holographic memory is given by the amount of data per page and the number of multiple recordings per unit area.
  • it is essential to increase the number of multiplexed recordings.
  • Block coding is used as a method for suppressing the bit error rate. Block coding is a method in which one page is divided into small areas, and a 0 or 1 signal is reconstructed therein.
  • 3:16 encoding or the like in which only 3 pixels are illuminated in a 4 ⁇ 4 (pixel) region is often used (see, for example, Patent Document 1).
  • the information amount per page is about 1 ⁇ 2.
  • the recording density of the holographic memory is given by the amount of data per page and the number of multiple recordings per unit area, the amount of information per page is improved in order to increase the recording capacity, and Therefore, it is necessary to reduce the bit error rate and increase the number of multiplexing.
  • the present invention improves the amount of information per page and increases the number of multiplexing by reducing the bit error rate in order to increase the recording capacity of the holographic memory. It is an object to provide a method, a recording method of a holographic memory, and a holographic memory device.
  • the present inventor regards data per page as data information of a plurality of stages having different resolutions by block coding, and each piece of data information is represented by one signal page data. It was invented to superimpose on. That is, in order to achieve the above object, the information encoding method of the holographic memory according to the first aspect of the present invention is to convert the information of the signal page data in the holographic memory into different stages of data by block encoding.
  • An information encoding method of a holographic memory in which each data is superimposed on one signal page data, wherein the different data includes at least light amplitude data and phase data, and the amplitude data is:
  • the phase data is 2 ⁇ s / n as s-th phase information for one of the binary data.
  • a phase is given (where n and s are natural numbers), and the other phase of the binary data has the same phase.
  • the information encoding method of the holographic memory of the first aspect it is possible to provide an optimum phase distribution when there are an odd number of ON bits in block encoding. That is, with the phase distribution information provided by the information encoding method of the first aspect, the amount of information per page can be increased by about 10%, the performance in multiplex recording can be improved, and the number of multiplexing can be increased. It becomes possible.
  • the phase data is block coding is 3: 9 coding or 3:16 coding, and there are three ON bits in the divided area.
  • the phase information a phase of 2 ⁇ s / n is given, and the same phase is given to the data signal value 1.
  • the ON bit existing in the divided area is a signal light of the holographic memory to which an ON / OFF bit pattern is added by an optical modulator, and the ON bits are arranged in a matrix of the optical modulator.
  • the pixel is in a state of transmitting light.
  • the OFF bit is in a state of blocking light among a large number of pixels arranged in a matrix of light modulators.
  • phase data is further added to the signal light of the holographic memory in addition to the amplitude data.
  • the signal light to which the amplitude data is added as information is transmitted through a phase modulation modulator.
  • One modulator may be capable of simultaneously modulating the phase and amplitude. It is also possible to realize a phase delay by controlling the polarization state. In that case, the phase is modulated after the amplitude is modulated.
  • a phase of 2 ⁇ s / n is assigned to one of the binary data as the phase information (for example, data value 0) as the s-th phase information, The same phase is given to the other (for example, data value 1).
  • the phase signal is given to each ON bit in the block of signal light to which the amplitude data is added as information, thereby obtaining an interference signal in the block. That is, a strong interference strength is obtained in the case of constructive interference within a block, whereas a weak interference strength is obtained in the case of constructive interference.
  • the obtained interference intensity is regarded as an intensity signal by threshold processing, and the signal value (0 or 1) of binary data is determined. If there are n odd numbers of ON bits in a block, giving different 2 ⁇ s / n phases (n and s are natural numbers) to each ON bit results in weak interference due to destructive interference in the block. Interference intensity. When viewed as an intensity signal, for example, information of data signal value 0 can be obtained.
  • each of the 3 ON bits for a data signal value 0 as phase information.
  • s-th s is 1, 2, 3 phase information
  • phases of 2 ⁇ / 3, 4 ⁇ / 3, and 2 ⁇ are added to each ON bit.
  • the same phase for the data signal value 1 as phase information, the same phase (for example, phase of ⁇ or 2 ⁇ ) is assigned to all three ON bits.
  • the information coding method of the present invention a new two-dimensional code based on phase information can be added in addition to the two-dimensional code based on the amplitude information.
  • the SN ratio of the signal values 0 and 1 is n 2 to 0. The maximum value can be given. For comparison, for example, in the case of modulation of 0 or ⁇ , the SN ratio is n 2 to 1.
  • phase information is not added or 0 or ⁇ is used as the phase information.
  • the individual pixel intensity in the block and the cell intensity for each block are increased, and the bit error rate of the pixel intensity and the cell intensity is improved.
  • the cell strength is a value obtained by squaring the sum of complex amplitudes of individual pixels in a block.
  • a second aspect of the present invention there is provided a method for encoding information of a holographic memory, wherein signal page data information in the holographic memory is regarded as different data in a plurality of stages by block encoding, and each piece of data is treated as one signal.
  • An information encoding method of a holographic memory superimposed on page data wherein the different data includes at least light amplitude data and phase data, and the amplitude data is divided into regions by block encoding,
  • the phase data is given a phase of ⁇ s or a phase of 2 ⁇ s / n as s-th phase information for one of the binary data (here, N and s are natural numbers), and the other phase of the binary data has the same phase.
  • the information encoding method of the holographic memory of the second aspect it is possible to provide an optimal phase distribution when there is an even number of ON bits in block encoding. That is, with the phase distribution information provided by the information encoding method of the second aspect, the amount of information per page can be increased by about 10%, the performance in multiplex recording can be improved, and the number of multiplexes can be increased. It becomes possible.
  • the phase data is block coding is 2: 4 coding or 4: 9 coding, and there are two ON bits in the divided area.
  • the phase information a phase of ⁇ s or a phase of 2 ⁇ s / n is given, and the same phase is given to the data signal value 1.
  • phase data is further added to the signal light of the holographic memory in addition to the amplitude data.
  • the signal light to which the amplitude data is added as information is transmitted through a phase modulation modulator.
  • One modulator may be capable of simultaneously modulating the phase and amplitude. In that case, the phase is modulated after the amplitude is modulated.
  • phase information for example, data value 0
  • phase information for example, data value 0
  • the phase information is given to each ON bit in the block of the signal light to which the amplitude data is added as information, so that the interference signal in the block The action to get.
  • the two-dimensional code by the phase can be added, and the amount of information per page increases.
  • each of the two ON bits is used for the data signal value 0 as phase information.
  • the assigned sth (s is 1, 2) phase information the phase of ⁇ s is added to each ON bit.
  • the same phase for the data signal value 1 as phase information, the same phase (for example, a phase of ⁇ or 2 ⁇ ) is assigned to all two ON bits.
  • the information encoding method of the holographic memory according to the second aspect has an SN ratio of the signal values 0 and 1 as the phase information of n 2 pairs as compared with the information encoding method of the holographic memory according to the first aspect. Therefore, the SN ratio of the phase information is slightly deteriorated.
  • Signal data can be two-dimensionally encoded as amplitude information.
  • the holographic memory device of the present invention is obtained by irradiating a disk-type recording medium with signal light and reference light to record image data as a light interference pattern and irradiating the disk-type recording medium with reference light.
  • a holographic memory device for reproducing data from a reproduced image comprising the following 1) to 5).
  • phase modulation means provided in the light guide path of signal light 5) Spatial shift multiplex recording means by displacement of reference light using an operation mechanism of an optical pickup system
  • phase modulation means of 4) described above is holographic amplitude
  • the operation mechanism of the optical pickup system means a rotating mechanism of the disc type recording medium and a moving mechanism of the disc type recording medium in the radial direction.
  • speckle shift multiplex recording means for multiplexing by displacement of the speckle reference light is used.
  • the speckle shift multiplex recording means multiplexes by using the shift Bragg selectivity by the speckle light used as the reference light by recording the signal light and the reference light while being spatially shifted. By slightly changing the position of the spot of the reference light, only the data having the same shift Bragg selectivity becomes diffracted light and can be read independently.
  • the holographic memory device of the present invention can add a new two-dimensional code based on phase information in addition to the two-dimensional code based on amplitude information by providing the phase modulation means of 4) above. Since 1-bit information can be added as interference intensity information by phase for each block in addition to the conventional two-dimensional code by amplitude, the amount of information per page increases. Also, the addition of phase information improves the bit error rate of pixel strength and cell strength, so that the number of multiplexing can be increased. Therefore, in the holographic memory device of the present invention, the recording capacity of the holographic memory can be increased as compared with the conventional device.
  • the phase modulation means of 4) described above is provided in the case where there are n even number of ON bits in the region where the holographic amplitude data is divided by block coding.
  • ⁇ s phase or 2 ⁇ s / n phase is given to one of binary data as s-th phase information (where n and s are natural numbers), and the same phase is given to the other binary data To do.
  • phase modulation means of 4 in addition to the two-dimensional code based on the amplitude information, a new two-dimensional code based on the phase information can be added.
  • the amount of information can be increased.
  • the addition of phase information improves the bit error rate of pixel strength and cell strength, and the number of multiplexing can be increased.
  • the SN ratio of the signal values 0 and 1 as the phase information is n 2 to 1, the SN ratio of the phase information is slightly deteriorated.
  • the confocal optical system by further comprising a confocal optical system, by using the confocal optical system, high frequency components are removed during recording, and only signal components are allowed to pass during reproduction to reduce crosstalk noise. It is preferable to increase the multiplex number.
  • a confocal optical system it is possible to remove high-frequency components with an aperture during recording and remove adjacent data with an aperture during reproduction, thereby reducing crosstalk noise.
  • the number of multiplexing can be increased. That is, by adding a two-dimensional code based on phase information in addition to a two-dimensional code based on amplitude information, the amount of information per page is increased, and further, the number of multiplexing is increased using a confocal optical system.
  • the recording capacity of the graphic memory can be increased.
  • the recording method of the holographic memory of the present invention uses the above-described information encoding method of the holographic memory of the present invention to increase the amount of information of one page data, perform spatial shift multiplex recording, and confocal optical system Is used to remove high frequency components during recording, pass only signal components during reproduction, and reduce crosstalk noise, thereby increasing the number of multiplexing and increasing the recording capacity of the holographic memory.
  • the spatial shift multiplex recording is a recording method in which a recording medium is moved by a small amount every time page data is recorded, and a relative positional deviation between the recording medium and reference light is used.
  • speckle shift multiplex recording is obtained by applying random phase modulation to reference light.
  • the present invention there is an effect that the amount of information per page of the holographic memory can be improved, and the number of multiplexing can be increased by reducing the bit error rate.
  • data per page is captured as data information of two different resolutions by block encoding.
  • the two-stage data information is amplitude data information and phase data information.
  • the data information of the amplitude data information and the phase data information the number of pixels used is different and the data has different resolutions.
  • These amplitude data information and phase data information can be superimposed on one signal page data.
  • the signal light of the holographic memory is given amplitude data after passing through the amplitude modulator.
  • the area of the signal light of the holographic memory is divided by block coding, and phase data is given to the ON bit of the divided block.
  • Table 1 below shows the coding rate (coding) according to the type of block coding (modulation code). rate).
  • Block coding indicates five types of 2: 4 coding, 2: 9 coding, 3: 9 coding, 4: 9 coding, and 3:16 coding.
  • the number of combinations that the amplitude data in one block in each block encoding can take as a code pattern is 6, 36, 84, 126, and 560.
  • the number of combinations that the phase data can take as a code pattern is 0 or 1 when it is determined by the threshold whether the phase data is weakened or strengthened by interference. Therefore, the number of combinations that one block can take as a code pattern in block coding is obtained by multiplying the number of combinations by amplitude data and the number of combinations of phase data, and becomes 12, 72, 168, 252 and 1120, respectively.
  • the number of bits that can be expressed in one block in block coding is as shown in the following (a) to (e).
  • the coding rate by each block coding is as shown in (A) to (E) below.
  • phase information to be superimposed on the 2: 4 encoded block will be described with reference to FIG.
  • the block encoding is 2: 4 encoding
  • a data signal value 0 is given as phase information to these two ON bits
  • the ON bit signal in the block causes destructive interference, and a weak interference intensity is obtained. Therefore, when the interference intensity obtained from the block is captured as an intensity signal by threshold processing, the signal value of binary data is 0.
  • the data signal value 1 is given as phase information to the two ON bits, the same phase is given to the two ON bits in the block.
  • the ON bit signal in the block causes constructive interference, and a strong interference strength is obtained. Therefore, when the interference intensity obtained from the block is regarded as an intensity signal by threshold processing, the signal value 1 of binary data is obtained.
  • FIG. 1 shows reproduction of 4 ⁇ 4 pixel image data in which 1 block (2 ⁇ 2 pixel image data) in which amplitude information and phase information are superimposed using 2: 4 encoding is arranged in 2 ⁇ 2 Amplitude information and phase information are extracted from the data, and a restoration signal is generated.
  • phase information to be superimposed on the 3:16 encoded block will be described with reference to FIG.
  • the block encoding is 3:16 encoding
  • the signal value of binary data is 0.
  • the data signal value 1 is given as the phase information to the three ON bits, the same phase is given to the three ON bits in the block.
  • the ON bit signal in the block causes constructive interference, and a strong interference strength is obtained. Therefore, when the interference intensity obtained from the block is regarded as an intensity signal by threshold processing, the signal value 1 of binary data is obtained.
  • FIG. 2 shows that for one block (4 ⁇ 4 pixel image data) in which amplitude information and phase information are superimposed using 3:16 encoding, amplitude information and phase information are extracted from reproduction data, It shows how it is generated.
  • FIG. 3 is an explanatory diagram of the information encoding method of the present invention (in the case of 3:16 encoding).
  • 3:16 encoding there are three ON bits in a 4 ⁇ 4 pixel block.
  • a data signal value 0 is given as phase information to three ON bits, a phase of 2 ⁇ / 3, 4 ⁇ / 3, 2 ⁇ is given to each ON bit.
  • a weak interference intensity is obtained.
  • the data signal value becomes 0.
  • the data signal value 1 is given as phase information to three ON bits, the same phase such as ⁇ or 2 ⁇ is given to the three ON bits in the block. Thereby, the ON bit signal in the block causes constructive interference, and a strong interference intensity is obtained.
  • the data signal value becomes 1.
  • FIG. 4 is a comparison graph of pixel intensity SNR (signal to noise ratio)
  • FIG. 5 is a comparison graph of SNR of cell intensity
  • FIG. 6 shows the pixel intensity BER (Bit FIG. 7 is a comparison graph of cell strength BER.
  • the horizontal axis represents the number of multiplexing of 10 to 100.
  • the pixel intensity SNR has improved SN in the 3:16 coding with phase information in addition to the amplitude information, compared to the 2: 4 coding with only amplitude information and no phase information.
  • the SN is improved in the case of 3:16 encoding in which different phases of 2 ⁇ s / n are given to the respective ON bits as compared with the case of modulation of 0 or ⁇ . This is because, by giving different 2 ⁇ s / n phases to each ON bit, the SN ratio of signal values 0 and 1 becomes n 2 to 0, whereas in the case of modulation of 0 or ⁇ This is because the SN ratio is n 2 to 1.
  • the SN of the cell strength SNR is improved in the 3:16 coding with the phase information in addition to the amplitude information, compared with the 2: 4 coding with only the amplitude information and no phase information.
  • the cell intensity is the square of the sum of complex amplitudes of individual pixels in the block.
  • 3:16 encoding the sum of complex amplitudes in 4 ⁇ 4 pixels is squared
  • 2: 4 encoding the sum of complex amplitudes in 2 ⁇ 2 pixels is squared.
  • the complex amplitude is expressed in the form of a ⁇ exp (i ⁇ b).
  • a is the amplitude
  • b is the phase.
  • the pixel intensity BER is poor in 2: 4 encoding with only amplitude information and no phase information, and 3:16 encoding with phase information in addition to amplitude information is independent of the phase to be applied, It is good.
  • the cell strength BER is the worst in 3:16 encoding (when the phase to be added is 0, ⁇ ), 2: 4 encoding and 3:16 encoding with only amplitude information and no phase information. (When the applied phase is 2 ⁇ / 3, 4 ⁇ / 3, 2 ⁇ ) is good. 3:16 encoding (when the phase to be applied is 2 ⁇ / 3, 4 ⁇ / 3, 2 ⁇ ) shows the best value.
  • 3:16 encoding (when the added phase is 2 ⁇ / 3, 4 ⁇ / 3, 2 ⁇ ) has the best SN for both pixel intensity and cell intensity, and bit error It can be seen that the rate is also good. Therefore, in the case of 3:16 coding, the phase of 0 and ⁇ is given to the three ON bits existing in the block by giving different phases of 2 ⁇ / 3, 4 ⁇ / 3, and 2 ⁇ . Rather than SN and bit error rate.
  • FIG. 9 shows a comparison graph of the reconstruction data of the pixel intensity in the simulation result.
  • FIG. 9 shows the SNR of the pixel intensity.
  • 10 and 11 show comparison graphs of reconstructed data of cell strength in the simulation results.
  • FIG. 10 shows the cell strength SNR
  • FIG. 11 shows the cell strength BER. From the graph of the pixel intensity SNR shown in FIG. 9, it can be seen that the SNR is improved by introducing phase modulation due to the influence of the residual diffraction efficiency. From the graph of the cell strength SNR shown in FIG. 10, it can be seen that even if the multiplexing number is 400, the SNR can be maintained at 2.0 or more. Further, from the graph of the cell strength BER shown in FIG. 10, when the allowable BER is 10%, it is understood that the allowable value is within the allowable range even if the multiplexing number is 400.
  • the analysis results by computer simulation are as follows.
  • the data size of the signal light is 512 ⁇ 512 pixels, and 128 blocks are formed by 3:16 encoding.
  • 3:16 encoding an information amount of 9 bits can be given only by amplitude information per block. For this reason, the information amount per page is 1152 (Byte) when only amplitude information is used, but increases to 1280 (Byte) when phase information is added to the amplitude information.
  • FIG. 8 shows a schematic diagram of a holographic memory device of the present invention.
  • the holographic memory device of the present invention is provided in a system for guiding the signal light 1 and the reference light 2 and aligning the polarization planes of the signal light 1 and the reference light 2 on the recording medium 6 and the light guide path of the signal light 1.
  • the amplitude light modulator 4 and the phase light modulator 5 provided in the light guide path of the signal light 1 are necessary.
  • Fourier transform is performed by the condenser lens 7a.
  • the condenser lens 7b In addition, in the home where the reproduction light 3 is reproduced from the recording medium 6, the Fourier transform is performed by the condenser lens 7b.
  • the recording medium 6 shown in FIG. 8 is divided into thin layers in order to express the volume effect of the hologram in performing numerical analysis, but it is not particularly necessary to divide into layers.
  • Example 2 it will be described that the recording density of the holographic memory can be improved by introducing a confocal optical system.
  • the advantages of the confocal optical system in the holographic memory are that a high-frequency component can be removed by an aperture during recording, and that adjacent data can be removed by an aperture during reproduction to pass only signal components and reduce crosstalk noise.
  • Holographic memory records high-density information in crystals and photopolymers. Since the spatial light modulation element which is a display element at the time of recording has a periodic structure, a high frequency component is generated. By removing this high-frequency component with an aperture, it is possible to eliminate excessive consumption of the photopolymer.
  • FIG. 12 shows single recording (see FIG. 12 (1)) and shift multiple recording (see FIG. 12 (2)) of the holographic memory.
  • Shift multiple recording unlike single recording, records a plurality of signal page data spatially superimposed in a photopolymer as a recording medium, with the distance to the null point (minimum point of diffracted light intensity) as the recording interval.
  • 1 is signal light
  • 2 is reference light
  • 3 is reproduction light
  • 5 is a random phase mask which is a phase light modulator
  • 6 is a recording medium
  • 8 is input signal page data.
  • shift multiplex recording speckle shift multiplex recording in which random phase modulation is applied to the reference light and the phase matching condition during reproduction is made stricter is used. Random phase modulation is composed of a phase modulator, a diffusion plate, a multimode fiber, or the like.
  • FIG. 13 shows a configuration diagram (development diagram) of the confocal optical system.
  • a confocal optical system has apertures arranged on both sides of the recording side and the reproducing side.
  • the recording side plays a role of cutting high-frequency components
  • the playback side plays a role of reducing crosstalk noise.
  • 7 is a condenser lens
  • 11a and 11b are an aperture on the recording side and an aperture on the reproduction side, respectively.
  • the signal light 1 from the input signal page data 8 passes through the condenser lens 7 and the aperture 11 a and is recorded on the recording medium 6.
  • the reproduction light 3 passes through the condenser lens 7 and the aperture 11b, and reproduces reproduction signal page data 9 with reduced crosstalk noise.
  • FIG. 14 shows a graph of the diffracted light intensity before and after passing through the aperture.
  • FIG. 14 (2) shows that after passing the aperture, only the signal component (reference numeral 1 in the figure) is allowed to pass and the crosstalk noise (reference numerals 2 and 3 in the figure) is reduced.
  • FIG. 15 shows how the crosstalk noise 12 is reduced from the reproduction light 3 during reproduction by using the aperture 11b.
  • FIG. 16 is a graph of the bit error rate with respect to the multiplex number (comparison graph with or without aperture).
  • the analysis condition parameters for simulation are shown in Table 3 below.
  • the bit error rate changes about three times depending on the presence or absence of the aperture. Further, it can be seen from the graph of FIG. 16 that if the allowable error rate is 1%, the multiplexable number can be increased from 45 to 71. Since the data amount per page is 8192 (bytes), it can be improved from 125.5 (GBe) to 197.9 (GBe) when converted to the recording capacity of a 5-inch disk. From this, it can be understood that the confocal optical system is effective.
  • the present invention is useful for encoding information in a holographic memory.
  • the holographic memory is aimed at realizing a recording capacity of 1 terabyte on a 5-inch disk. Therefore, the upper limit value of the capacity needs to be about 10 terabytes. To that end, the present invention is useful because the recording capacity can be improved as compared with the conventional method.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Signal Processing (AREA)
  • Optical Recording Or Reproduction (AREA)
  • Holo Graphy (AREA)
  • Signal Processing For Digital Recording And Reproducing (AREA)

Abstract

L'invention porte sur un procédé de codage d'informations et un dispositif de mémoire holographique qui augmentent le volume d'informations par page de mémoire holographique et réduisent le taux d'erreurs sur les bits afin d'assurer un facteur de multiplexage plus élevé. Le procédé de codage d'informations de mémoire holographique consiste à capturer des informations concernant des données de page de signal dans une mémoire holographique sous la forme de différentes données d'une pluralité d'étages par codage en bloc, et à superposer chaque donnée sur une page unique de données de page de signal. Les différentes données d'une pluralité d'étages comprennent des données d'amplitude et des données de phase optiques. Des données d'amplitude sont divisées par zone par codage en bloc. Lorsqu'il existe un nombre n de bits activés de numéro impair dans une zone divisée dans les données de phase, une phase de 2πs/n (n et s étant des entiers naturels) est communiquée en tant que sième informations de phase à un seul ensemble de données binaires, et la même phase est communiquée à l'autre ensemble de données binaires.
PCT/JP2012/005161 2011-08-15 2012-08-15 Procédé de codage d'informations de mémoire holographique, procédé d'enregistrement de mémoire holographique et dispositif de mémoire holographique WO2013024596A1 (fr)

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JP2013528920A JP5896362B2 (ja) 2011-08-15 2012-08-15 ホログラフィックメモリの情報符号化方法、ホログラフィックメモリの記録方法およびホログラフィックメモリ装置

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